1. Field of the Invention:
The present invention relates to a variable-displacement turbine, and more particularly to a variable-displacement turbine for use in a turbocharger for use with an engine for an automobile or the like.
2. Description of the Relevant Art:
Variable-displacement turbines are used as exhaust turbines of variable-displacement turbochargers. One such variable-displacement turbine is disclosed in Japanese Patent Publication No. 38-7653.
The disclosed variable-displacement turbine has a turbine housing accommodating a turbine wheel therein and including a pair of parallel annular walls defining therebetween a passage for supplying and guiding a fluid (exhaust gases) to the turbine wheel from its outer periphery. An annular array of movable vanes is disposed between the walls of the turbine housing in surrounding relation to the turbine wheel, the movable vanes providing variable restrictions for passage of the fluid therethrough.
When the engine operates in a low-speed range, the movable vanes are tilted to reduce the opening of the variable restrictions to increase the supercharging effect in the low-speed range. Because the variable restrictions or nozzles are defined between the movable vanes, however, the opening of the variable restrictions is greatly affected by even a small change in the angle of inclination of the movable vanes. As a result, the opening of the variable restrictions cannot accurately be controlled insofar as the opening is relatively small.
Since the turbine housing and movable vanes in a general variable-displacement turbine are exposed to a stream of high-temperature exhaust gases, the turbine housing and movable vanes are subject to thermal strain, and hence the movable vanes may not smoothly be actuated.